Attention Deficit Disorder (ADD) and Attention Deficit/Hyperactivity Disorder (ADHD) (severally and collectively hereinafter referred to as "AD") are developmental disorders of self-control. They consist of problems with attention span, impulse control and activity level. These problems are reflected in impairment of a person's will or capacity to control his or her own behavior relative to the passage of time and to keep future goals and consequences in mind.
Traditionally, methylphenidate has been used as the drug of choice for the treatment of AD in both children and adults for several reasons. Methylphenidate, described in U.S. Pat. No. 2,957,880, is a central nervous system stimulant. Though not an amphetamine, methylphenidate functions in a similar way in the brain. The current commercially available dosage form (Ritalin.RTM. tablets) and available strengths of the tablets fall short of providing effective treatment for a significant portion of the patient's waking hours. Methylphenidate has a short duration of action of from about 2 to 4 hours. A controlled release tablet of methylphenidate is commercially available, but is available only in one strength. This product, which was designed to eliminate the need for multiple administration of a tablet during the school day for children and reduce dosing to either once or twice a day, falls short of providing effective treatment for a significant portion of the patient's waking hours.
The regimen of methylphenidate currently used for ADHD exhibits numerous shortcomings that include fluctuations in blood levels with immediate release tablets; inconvenience of successfully complying with more frequent dosing (for examples, inability of children to accurately monitor time and/or stigma of medication); difficulty for young children to swallow tablets whole; availability of only two types of tablets available, immediate release tablets and sustained release tablets, ineffectiveness of BID (behavioral inhibition disorder) dosing for a significant portion of the patient's waking hours; and potential for drug abuse.
Topical application of drugs provides many advantages over conventional oral administration. Advantages include convenience, uninterrupted therapy, improved patient compliance, ease of discontinuance, elimination of hepatic first pass metabolism, a high degree of control over blood concentration of the drug and improved overall therapy.
The term "topical" or "topically" is used herein in its conventional meaning as referring to direct contact with a spot on a mammal, which can be any anatomical site or surface area including skin or mucous membranes, or hardened tissue such as teeth or nails.
The term "application" is intended to mean any mode which results in systemic administration.
The term "mucosa" or "mucosal" as used herein means oral, buccal, vaginal, rectal, nasal, intestinal, and ophthalmic surfaces.
Although topical application systems have many advantages, most drugs do not readily lend themselves to this mode of administration due to the well known barrier properties of the skin. Molecules moving from the environment into and through intact skin must first penetrate the stratum corneum, the outer horny layer of the skin, and any material on its surface. The molecule must then penetrate the viable epidermis and the papillary dermis before passing through the capillary walls and into the systemic circulation. Along the way, each of the above-mentioned tissues will exhibit a different resistance to penetration by the same molecule. However, it is the stratum corneum, a complex structure of compact keratinized cell remnants separated by extracellualar lipid domains, that presents the greatest barrier to absorption of topical compositions or transdermally administered drugs.
There are topical application systems known in the art which provide a means for transdermal delivery of various drugs where methylphenidate is mentioned, e.g., in Quan et al., U.S. Pat. No. 5,601,839, a transdermal delivery system is disclosed. A basic drug having a pKa of 8.0 or greater is incorporated into the delivery system. The formulation also requires the use of triacetin as a permeation enhancer. Quan et al. lists oxybutynin, scopolamine, fluoxetine, epinephrine, morphine, hydromorphone, atropine, cocaine, buprenorphine, chlorpromazine, imipramine, desipramine, methylphenidate, methamphetamine, lidocaine, procaine, pindolol, nadolol, and carisoprodol as preferred "basic drugs." Bloom et al., U.S. Pat. No. 5,614,178, discloses a composition for topical delivery comprising an effective amount of a pharmaceutically active substance, a high molecular weight crosslinked cationic polymer, a non-ionic surfactant, an alkoxylated ether and a pharmaceutically acceptable carrier. Bloom et al. includes a myriad of different drugs for incorporation into the topical delivery system. Lee et al., U.S. Pat. No. 5,629,019 discloses a transdermal delivery composition containing a hydrophobic permeation enhancer, which permeation enhancer has been micronized and stabilized in an inert carrier. These compositions can include a biologically active substance to provide enhanced permeability of the active agent to the skin or mucosa. Lee et al. lists over 100 beneficial agents to be included in the transdermal delivery composition.
Therefore, despite the existence of many different types of topical application systems in the art, there remains a continuing need for improving the method of delivery of methylphenidate to a patient. Accordingly, a new topical application system whereby delivery of the active substance, herein methylphenidate, achieves substantially zero-order kinetics over a time period of at least 10 hours has been developed.